PROBLEMS AFTER TIMING BELT/W PUMP CHANG

after I put my 2001 1.4 renault scenc into the garage to get w/pump and alternater belt, timing belt replaced (about 1-2 months ago) I noticed that after the cars been lying for a few hours that when I start the engine the revs are sitting just above 1000 revs after approx 10-15 mins of driving it returns to about 500 revs. Also in this time there is a strange rubbing/grinding noise that is coming from either the alternator componments or timing belt casing but not sure which now iv noticed aswell as the above before I drive it as I reverse out of my space and put it into first gear and try to accelerate gently the car is jerking this is only happening first time of starting the car after its been idle overnight or a long period of time. Any advice would be much appreciated thank you, john

The starting idle is fine. In cold weather it will idle high for a few minutes. You could check for vacuum line leaks?. Have the garage that repaired the vehicle check the rubbing/grinding noise. It could be the alternator bearings worn. It could also be the timing belt tensioner is bad or belt incorrectly fitted, which could damage engine if not corrected